Viscoelastic properties of monodisperse star polymers in short linear matrix

Taghipour, Hamid [UCL] Van Ruymbeke, Evelyne [UCL]

In this analysis, we validate predictions of one of the progressive tube based models namely, the TMA model by van Ruymbeke et al. (Macromolecules. 2012, 45, 2085), against linear viscoelastic dynamic rheology data of binary blends of nearly monodisperse 1, 4-polybuadiene symmetric 3-arm star Mw = 76 kg/mol and monodisperse short linear chains Mw = 7.5 kg/mol which is previously published by Schivokhin et al. In such a case, besides increasing of the modulus level of the binary blends at intermediate and low frequency, the terminal region indicated that at low proportions of star chains, these last ones relax much faster than the corresponding monodisperse sample of same architecture. This fast relaxation is due to the constraint release effect of the linear component which is already relaxed and plays no more role in the constraining tube. In such conditions, the linear chains behave as a solvent for the star chains. In particular according to the original TMA the short linear chains will relax by reptation and arm retraction along their primitive path while the starlike chains will renew orientation by CLF. Within this framework the non-relaxed fraction of star chains at time t is determined, based on the depth of the molecular segments and accounting for the solvent effect from the linear chains. This result is in agreement with the experimental data. We also show that the constraint-release-Rouse relaxation process, which allows the star chains to relax by Rouse, but at the rhythm of the entanglement/disentanglement of the linear chains, is of prime importance for these sample. This molecular scenario is proved to be the dominant process of the star relaxation.